Merge pull request #572 from evoskuil/master

Optimize tail end of catch-up downloads with stall message.

include/bitcoin/node/chasers/chaser.hpp

@@ -59,10 +59,14 @@ class BCN_API chaser
         /// Issued by 'block_in_31800' and handled by 'session_outbound'.
         starved,
 
-        /// Channel is directed to split its work and stop (channel_t).
+        /// Channel (slow) is directed to split its work and stop (channel_t).
         /// Issued by 'session_outbound' and handled by 'block_in_31800'.
         split,
 
+        /// Channels (all with work) are directed to split work and stop (0).
+        /// Issued by 'session_outbound' and handled by 'block_in_31800'.
+        stall,
+
         /// A block has been downloaded, checked and stored (height_t).
         /// Issued by 'block_in_31800' and handled by 'connect'.
         checked,

include/bitcoin/node/impl/chasers/chaser_organize.ipp

@@ -475,6 +475,7 @@ void CLASS::do_organize(typename Block::cptr& block_ptr,
     else
     {
         // Delay so headers can get current before block download starts.
+        // Checking currency before notify also avoids excessive work backlog.
         if (is_current(header.timestamp()))
             notify(error::success, chase::header, point);
     }

src/chasers/chaser_header.cpp

@@ -74,7 +74,6 @@ bool chaser_header::is_storable(const system::chain::header& header,
             state.cumulative_work() >= settings().minimum_work);
 }
 
-
 } // namespace database
 } // namespace libbitcoin
 

src/protocols/protocol_block_in_31800.cpp

@@ -225,6 +225,15 @@ void protocol_block_in_31800::handle_event(const code&,
             POST(do_split, channel);
         }
     }
+
+    // If this channel has work, split it and stop.
+    else if (event_ == chaser::chase::stall)
+    {
+        if (!map_->empty())
+        {
+            POST(do_split, chaser::count_t{});
+        }
+    }
 }
 
 void protocol_block_in_31800::do_get_downloads(chaser::count_t) NOEXCEPT

src/sessions/session_outbound.cpp

@@ -107,7 +107,11 @@ void session_outbound::split(chaser::channel_t) NOEXCEPT
         const auto channel = slowest->first;
         speeds_.erase(slowest);
         node::session::notify(error::success, chaser::chase::split, channel);
+        return;
     }
+
+    // With no speeds recorded there may still be channels with work.
+    node::session::notify(error::success, chaser::chase::stall, {});
 }
 
 // performance